1. Field of the Invention
The present invention relates to an apparatus and method for electrodepositing material on an article. More particularly, the present invention relates to continuously electrodepositing material on semiconductor components by retaining the components on a moving cathode immersed in an appropriate electrolyte wherein a wire mesh anode rotates about the moving cathode during electrodeposition.
2. State of the Art
Semiconductor wafers, substrates, and printed circuit boards (collectively hereinafter xe2x80x9csemiconductor substratesxe2x80x9d) are often coated with various materials, such as metals, which are etched in later semiconductor fabrication processes to form components on the semiconductor substrates. Techniques for coating semiconductor substrates include electrodeposition, electron beam evaporator deposition, chemical vapor deposition, sputter deposition, and the like. Electrodeposition has become a commonly used technology.
Electrodeposition is a process which deposits a thin film of material, such as metal or metal alloy, on an article. In electrodeposition, as shown in prior art FIG. 6, an article 202 is placed in a tank 204 containing an appropriate deposition solution, such as electrolyte solution 206, which contains ions 208 of the metal to be deposited on the article 202. The article 202 forms a cathode or is in electrical contact with a cathode 210 which is immersed in the electrolyte solution 206. The cathode 210 is connected to a negative terminal 212 of a power supply 214. A suitable anode 216 is also immersed in the electrolyte solution 206 at an appropriate distance from the cathode 210 and is connected to a positive terminal 218 of the power supply 214. The power supply 214 generates an electrical current which flows between the anode 216 and the cathode 210 through the electrolyte solution 206. The electrical current causes an electrochemical reaction at the surface of the article 202 which results in the metal ions 208 in the electrolyte solution 206 being deposited on the article 202.
With semiconductor components, it is desirable to deposit the metal film with a uniform thickness across the article and with uniformity of composition of the metal(s) and/or other compounds forming the metal film. However, the electrodeposition process is relatively complex and various naturally occurring forces may result in a degradation in the electrodeposition process. The electrical current or flux path between the anode and the cathode should be uniform without undesirable spreading or curving to ensure uniform deposition. Additionally, since the metal ions in the deposition solution are deposited on the article, the deposition solution becomes depleted of metal ions which degrades the electrodeposition process. Therefore, suitable controls are required to introduce metal ions into the deposition solution in order to maintain consistency.
U.S. Pat. No. 5,516,412, issued May 14, 1996 to Andricacos et al. (the ""412 patent), relates to an electrodeposition cell having a rack for vertically supporting a silicon substrate to be electrodeposited. A paddle is disposed within the electrodeposition cell for agitating an electrolyte solution within the cell to maintain a uniform distribution of deposition material within the electrolyte solution. Furthermore, the ""412 patent teaches that the rack can be designed to be removable for automated handling. Although the ""412 patent addresses the control issues discussed above, the rack assembly disclosed is not conducive to high-volume manufacturing. Furthermore, the ""412 patent does not teach or suggest any means for improving the deposition on the silicon substrate by the movement of either the anode or cathode.
U.S. Pat. No. 4,696,729, issued Sep. 29, 1987 to Santini, and U.S. Pat. No. 5,198,089, issued Mar. 30, 1993 to Brueggman, both relate to an electrodeposition cell having a cathode assembly which is vertically mounted and holds a plurality of semiconductor substrates to be coated, and an anode which is also vertically mounted adjacent to the cathode assembly. The deposition solution is pumped upward between the anode and the cathode to produce a laminar flow across the surface of each wafer. However, both patents lack a means for insuring uniform distribution of deposition material within the deposition solution.
Systems which can be used for electrodeposition can also be used for electropolishing and electroetching. For example, U.S. Pat. No. 5,096,550, issued Mar. 17, 1992 to Mayer et al. (the ""550 patent), teaches attaching an article to a rotating anode positioned horizontally face down in a polishing or etching bath. However, the ""550 patent teaches only the motion of the cathode and since the articles are attached one at a time in the anode, the apparatus of the ""550 patent is not conducive to high-volume manufacturing.
In most electrodeposition techniques, the wafers are attached to the cathode. The attachment of the wafers to the cathode can lead to significant problems, especially as the wafer quantities are increased within a single batch, such as control of the thickness of the material on the wafer. The problem of material thickness control is brought about by the non-uniformity of metal ions and less uniform current density in the electrolyte solution.
It is desirable to provide highly uniform thickness and composition of deposition material on an electrodeposited article or to uniformly polish or etch an article. Furthermore, it is also desirable to do so in an apparatus capable of high-volume manufacturing, preferably using automated handling equipment.
The apparatus of the present invention may comprise a housing tank containing a reaction solution, such as a deposition solution (e.g., an electrolyte solution). A moving cathode travels through a hollow anode which are both immersed in the reaction solution. The hollow anode is in electrical communication with a positive terminal of a power supply. The cathode is in electrical communication with a negative terminal of the power supply. The hollow anode is preferably a rotatable wire mesh cylinder which is rotated by a variable speed and direction motor. The wire mesh allows the reaction solution to flow through the anode. The rotation of the hollow anode agitates and mixes the reaction solution to maintain a uniform distribution of deposition material, etching material, or polishing material within the reaction solution. It is, of course, understood that the hollow anode can be any perforated metal structure, such as a thin sheet of metal, with a plurality of holes drilled therethrough. The rotation also prevents any dead spots on the anode from affecting the uniformity. Dead spots are considered as points where a complete electrical path between the anode and the cathode is not possible due to contamination or other imperfections on the anode.
The moving cathode is preferably a continuously moving structure to which the semiconductor substrates are mounted. The moving cathode is preferably a belt, interlinked moving housings on a cabling system, or the like. The moving cathode includes a plurality of article retainers, such as clips, for retaining the semiconductor substrates. It is preferred that the semiconductor substrates are mounted to the moving cathode mounting surface such that they are vertical or face downward so that debris from the electroplating (as well as electroetching or electropolishing) reaction does not build up on and contaminate the semiconductor substrates. Most preferably, the moving cathode has multiple moving surfaces which move in a corkscrew path, so that semiconductor substrates pivot about the radius of the cathode to prevent debris from the electroplating reaction from contaminating the semiconductor substrate surfaces.
The present invention is also useful for electrophoretic deposition, such as discussed in U.S. Pat. No. 3,714,011, issued Jan. 30, 1973 to Grosso et al. (electrophoretic deposition of cathodoluminescent material), and U.S. Pat. No. 4,592,816, issued Jun. 3, 1986 to Emmons et al. (electrophoretically depositing a photosensitive polymer composition on a conductive substrate), photoresist deposition, cleaning/polishing surfaces, or etching surfaces, such as discussed in U.S. Pat. No. 5,096,550, issued Mar. 17, 1992 to Mayer et al. In cleaning/polishing and etching of semiconductor substrates, the solution in which the semiconductor substrates are immersed may react in the presence of the electrical current and heat to activate an electrochemical reaction on the semiconductor substrate for cleaning or etching. Of course, with cleaning/polishing and etching of a semiconductor, the anode becomes the cathode and vice versa by switching the electrical connectors. In etching, the semiconductor substrate may be etched by any conventional etching techniques, such as masking the semiconductor substrate and inserting the semiconductor substrate into the apparatus for etching down to etch stops on the semiconductor substrate.
The controllable parameters of apparatus of the present invention may be monitored and controlled by a variety of means. The concentration of the reaction material and pH level in the reaction solution may be monitored by sensors and controlled by adding additional reaction material and/or acid/base to maintain said concentration and PH levels, respectively. The temperature of the reaction solution may be monitored and adjusted with a heat or cooling source within or adjacent to the reaction solution. The flux path between the anode and the cathode may be monitored and adjusted by varying the voltage from the power supply to the anode and the cathode. Also, electrical conductive surfaces to be plated can be tied together electrically to enable coating to be achieved on the various patterns that are otherwise isolated and would require an individual electrical bias.
The present invention achieves a highly uniform thickness and composition of deposition material on an article, and may also be used to achieve a uniform etch or polish on an article.